Decorator pattern

The Decorator Design Pattern is a structural design pattern that allows you to add new behaviors or functionalities to objects dynamically.

public interface Coffee {
    String getDescription();
    double cost();
}
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public abstract class CoffeeDecorator implements Coffee{
    protected final Coffee coffeeDecorator;

    public CoffeeDecorator(Coffee coffeeDecorator) {
        this.coffeeDecorator = coffeeDecorator;
    }

    @Override
    public String getDescription() {
        return coffeeDecorator.getDescription();
    }
}
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public class SimpleCoffee implements Coffee{
    @Override
    public String getDescription() {
        return "Simple coffee";
    }
    @Override
    public double cost() {
        return 20;
    }
}

public class WithMilk extends CoffeeDecorator {
    public WithMilk(Coffee coffeeDecorator) {
        super(coffeeDecorator);
    }

    @Override
    public String getDescription() {
        return super.getDescription() + ", With milk";
    }

    @Override
    public double cost() {
        return coffeeDecorator.cost() + 10;
    }
}

public class WithSugar extends CoffeeDecorator{
    public WithSugar(Coffee coffeeDecorator) {
        super(coffeeDecorator);
    }

    @Override
    public String getDescription() {
        return coffeeDecorator.getDescription()+",With sugar";
    }

    @Override
    public double cost() {
        return coffeeDecorator.cost()+5;
    }
}
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When to use

1. Adding Responsibilities Dynamically
2. Avoiding Subclass Explosion

Check full code in github